The slip distribution of the 1992 Nicaragua earthquake from tsunami run-up data

The 2 September 1992 Nicaragua tsunami was induced by an M(S) similar or equal to 7 - 7.3 earthquake and caused about 170 victims and significant damage to the coastal areas. The aim of this work is to infer the slip distribution along the causative seismic fault from the available tsunami run-up field data. We have subdivided the fault plane into five slip-independent subfaults and computed the corresponding numerical Green's functions by integrating shallow-water equations via a finite-element technique. The slip distribution on the fault has been determined by applying a least-squares procedure to the differences between the observed run-up values and the computed maximum water levels along the coast. The main result is that the best fit is found for a nonuniform coseismic slip, with the highest displacement taking place in the southernmost part of the fault. The measure of the improvement is given by the global rms residual of the heterogeneous-slip case being circa 25% smaller than that of the uniform case. An ancillary outcome of the analysis is the evaluation of the mean amplification factor of the tsunami wave investing the Nicaraguan coast, that, on assuming a rigidity of 1 x 10(10) N/m(2), results to be 3.45.